It is often necessary to detect the following state of a solid or liquid substance existing in a pipe, the outer surface of which is exposed:
(1) In a pipe charged with concrete, a state of charging of said concrete;
(2) In a pipe serving as a trough in a plant building, a state of accumulation of dust;
(3) In a pipe in which a liquid exists, a level of the surface of said liquid; and
(4) In a pipe having a neck portion where the cross-sectional area of the pipe is sharply reduced, and through which a liquid is flowing, a position of occurrence of a cavity at said neck portion.
The following methods are known for detecting a state of charging of concrete in a pipe charged with concrete, or state of accumulation of dust in a pipe serving as a trough:
(A) Detecting method using radioactive rays:
This method comprises: projecting radioactive rays such as X-ray or gamma-ray toward a pipe to be tested from the side of the outer surface thereof, measuring an amount of radioactive rays having passed through the pipe, and detecting a state of charging of concrete in the pipe or a state of accumulation of dust in the pipe by means of the thus measured amount of transmission of the radioactive rays.
(B) Detecting method using ultrasonic waves:
This method comprises: transmitting ultrasonic waves toward a pipe to be tested from the side of the outer surface thereof, receiving reflected waves of the transmitted ultrasonic waves, measuring a period of time required up to receiving of the reflected waves of the transmitted ultrasonic waves, and detecting a state of charging of concrete in the pipe or a state of accumulation of dust in the pipe by means of the period of time required up to receiving of the reflected waves.
(C) Detecting method based on knocking:
This method comprises: knocking a pipe to be tested from the side of the outer surface thereof with a hammer, for example, and detecting a state of charging of concrete in the pipe or a state of accumulation of dust in the pipe by means of the thus produced sound.
(D) Detecting method based on cutting:
This method comprises: cutting out a pipe to be tested to permit an operator to observe directly the inner surface of the pipe, thereby detecting a state of accumulation of dust in the pipe.
The detecting method using radioactive rays as mentioned in (A) above has the following problems:
(a) Detecting operation cannot be conducted unless the operator is qualified for handling radioactive rays. There is therefore a limitation in personnel.
(b) It is difficult to make a proper judgement on the result of detection, requiring high-level experience and technical knowledge.
(c) Detecting operation can be carried out only at a position closest to the outer surface of the pipe. When the pipe is installed at an elevated position apart from the ground, therefore, it is necessary to provide a scaffold for detecting operation.
(d) The range of a single run of detection is narrow. It thus requires much time and labor for detecting operation, leading to a low operating efficiency.
The detecting method using ultrasonic waves as mentioned in (B) above has the following problems:
(a) An error is often contained in the result of detection, thus preventing accurate detection.
(b) Detecting operation can be carried out only at a position in contact with the outer surface of the pipe. When the pipe is installed at an elevated position apart from the ground, therefore, it is necessary to provide a scaffold for detecting operation.
(c) The range of a single run of detection, being only a point, is very narrow. It thus requires much time and labor for detecting operation, leading to a low operating efficiency.
The detecting method based on knocking as mentioned in (C) above has the following problems:
(a) Determination of a state of a substance existing in the pipe requires high-level experience and technical knowledge, with furthermore much differences between individual operators, thus impairing accurate detection of a state of the substance existing in the pipe.
(b) Detecting operation can be carried out only at a position closest to the outer surface of the pipe. When the pipe is installed at an elevated position apart from the ground, therefore, it is necessary to provide a scaffold for detecting operation.
(c) Detecting operation requires much time and labor, resulting in a low operating efficiency.
The detecting method based on cutting as mentioned in (D) above has the following problems:
(a) Use of the pipe must be interrupted for a while during cutting and detecting operations, and these cutting, detecting and restoring operations require much time and labor, resulting in a low operating efficiency.
(b) When the pipe is installed at an elevated position apart from the ground, it is necessary to provide a scaffold for detecting operation.
For a pipe, having a neck portion where the cross-sectional area of the pipe is sharply reduced, and through which a liquid is flowing, a method is known for detecting a position of occurrence of a cavity at the neck portion, which comprises: receiving ultrasonic waves produced upon disappearance of a cavity produced at the neck portion of the pipe by means of an underwater microphone installed in the pipe, and detecting a position of occurrence of the cavity by means of an acoustic pressure level of the thus received ultrasonic waves.
The abovementioned method for detecting the cavity has the following problems:
(a) It is difficult to make a proper judgement on the result of detection, requiring high-level experience and technical knowledge.
(b) An accurate position of occurrence of the cavity cannot be detected, and it is impossible to detect an accurate magnitude of the cavity.
(c) The underwater microphone installed in the pipe impairs smooth flow of the liquid through the pipe.
An appropriate method for detecting a level of the surface of a liquid existing in a pipe is not known.
Under such circumstances, there is a strong demand for development of a method which permits certain, easy and efficient detection of a state of a solid or liquid substance existing in a pipe, the outer surface of which is exposed, at a position apart from the pipe in a non-contact manner without the need for a special qualification, but a method provided with such properties has not as yet been proposed.